Introduction

The absence of electric power greatly constrains a community's ability to generate income and provide local services. Decentralised energy options using local resources, such as wind, biogas, solar power and hydro power, offer many advantages for meeting the needs of rural populations. Development of one or more renewable energy options can improves both of these aspects of community life

Since the early 1990s, pico-hydro has been used to deliver electricity and mechanical power to remote mountainous areas of the world. Pico-hydro projects are hydroelectric schemes with a power generation capacity of up to 5 kilowatts (kW). The energy in water flowing down a slope is converted into electrical energy. Pico-hydro schemes have low power outputs, but require little water and are simple to install. They typically provide energy for lighting and battery charging.

Experts from the Energy Programme of ITDG East Africa, based in Kenya, in collaboration with Nottingham Trent University in the UK are working to develop the pico-hydro power sector in Kenya. The project demonstrates that pico-hydro technology is a sustainable and affordable technology for community electrification. Contributing to the establishment of hydro power infrastructure in rural Kenya and sub-Saharan Africa as a whole, the project benefits two rural communities in Kirinyaga District, central Kenya.

Water Power

The flow of water in rivers and streams is a potential source of energy. Hydro power is a very clean source of energy. It relies on a natural, non-polluting and renewable resource. Traditional water-wheels, used for providing energy for milling and pumping, have been superseded by modern turbines that are compact, highly efficient and capable of turning at high speed.

Hydro power has many advantages, including:

Power is usually available continuously on demand.

It is a concentrated energy source.

The energy available is predictable.

No fuel and limited maintenance are required, so running costs are low compared with diesel power.

It is a long-lasting and robust technology; systems can last for 50 years or more without major new investments.

Micro-hydro is the term used for technologies that convert energy in flowing water to direct-drive shaft power or to electricity generation on a very small scale. Ranging from a few hundred watts for battery charging or food processing applications up to 100 kW, micro-hydro provides power for small communities and rural industry in remote areas away from grid electricity. Hydro power that produces a maximum electrical output of 5 kW is called pico-hydro.

Pico-hydro Power

Recent innovations in pico-hydro technology have made it a source of power for some of the poorest and most remote regions in the world. It is a versatile power source as it can produce alternating current (AC) electricity, enabling standard appliances to be used, and it can be distributed to a whole village. It is used to power light bulbs, radios, televisions, refrigerators and food processors. It offers communities an alternative to the use of hazardous and expensive kerosene for lighting households, schools and businesses. Mechanical power can also be used with some designs to operate workshop tools and grain mills.

Pico-hydro has a number of advantages over larger systems.

Smaller water flows are required and there are many more sites that are suitable.

It is easier to establish and maintain agreements regarding ownership, payments, operation, maintenance and water rights, as the units only supply power for a small number of households.

Even in countries with extensive grid electrification, pico-hydro can be suitable for the many small, remote communities for which grid extension would be extremely expensive and not practical.

Locally manufactured systems can be produced that have much lower long- term costs per kilowatt than solar, wind and diesel systems.

Pico-hydro in Kenya

Kathamba and Thima, in the Kirinyaga District of Kenya, are the recipients of a pico-hydro scheme, the first of its kind in Africa, thanks to ITDG East Africa and Nottingham Trent University's Pico Hydro Unit. The success of the project is due to the availability of trained people and the support given by the local communities.

In Kathamba during the wet season, the spring produces 8 litres of water per second, generating approximately 1.7 kW to 2 kW of power. This is distributed to more than 30 households, with another 35 homes awaiting connection. The scheme in Thima covers 66 households. Each 'package' consists of light units and a socket for which users pay between US$55 and $75 to be connected to electricity. Fuel costs have dramatically reduced, with money saved each month on kerosene and dry cell batteries.

Powerhouse and community in Ndundu Village, Thima

Eric Mucharia and family at home watching TV

How Does it Work?

Water is diverted down a pipe, called the penstock, to fall through a vertical height or head, in order to gather energy. The lower end of the penstock is attached to a turbine that is turned by the energy in the falling water. As the turbine spins, it can be connected either directly to machines such as mills and presses or to a generator to provide electrical power for a small grid or battery charging. The amount of energy available is directly related to the volume of water flowing down the penstock and the height, through which it falls. The greater the volume of water and the greater the height, the more energy can be harnessed.

Water supply
The source of water is a stream or an irrigation channel. Small amounts of water can also be diverted from rivers. It is important that the source of water is reliable and not needed by anyone else. Springs make excellent sources as they do not dry up in dry weather and are usually clean, which stops silt building up in the system.

Forebay tank
Water is fed into a forebay tank. This is often enlarged to form a small reservoir. This can be useful if the water available is not enough during the dry season.

Penstock pipe
Water flows from the forebay tank or reservoir down a long pipe called the penstock. At the end of the penstock water comes out of a nozzle as a high- pressure jet. A drop or head of at least 20 metres is recommended and means that the amount of water needed to produce enough power for the basic needs of a village is quite small.

Turbine and generator
The power in the jet, or hydro power, is transmitted to a turbine runner that changes it into mechanical power. The runner has blades or buckets that cause it to rotate when struck by the water. The turbine is a general name that refers to the runner, nozzle and surrounding case. The runner typically spins 1500 times every minute. The turbine is attached to a generator. This converts rotating power into electrical power. This is how water flowing in a small stream can become electricity.
A pico generator

Electronic controller
An electronic controller is connected to the generator. This matches the electrical power that is produced to the electrical loads that are connected, and stops the voltage from changing as devices are switched on and off.
An electronic load controller

Mechanical load
The mechanical load is a machine connected to the turbine shaft using a pulley system so that power can be drawn directly from the turbine. The rotating force of the turbine runner can be used to turn equipment such as grain mills or woodwork machinery. Approximately 10 per cent of the mechanical power is lost in the pulley system but it is still an efficient way of using the power as none is lost in the generator or electric motor.

Distribution system
The distribution system connects the electricity supply from the generator to the houses or schools. This is often one of the most expensive parts of the system.

Electrical loads
Electrical loads are usually connected inside houses. This is a general name given to any device that uses the electricity generated. The type of loads connected to a pico-hydro scheme depends largely on the amount of power generated. Using the power wisely can add more benefits. Special lights such a fluorescent bulbs, for example, use less power and so more lights can be connected to the same generator.

After passing through the whole system, water is normally returned to a stream or river below the powerhouse.

Planning a Pico-hydro Scheme

It is important to conduct a feasibility study in a proposed area to determine what is required to implement a pico-hydro project for village electrification.

Overview: Establish the demand, willingness to pay, local ability to manage a scheme, and grid electricity available or planned.Location: A suitable geographical location for a pico-hydro scheme is one with steep rivers that have an all-year flow.Demand survey: Estimate the number of houses within 1km (approximately two- thirds of a mile) from the water supply and those who are willing to pay. A 1km radius is the distance that electricity can most easily be transmitted.Power estimate: The head and flow rate should both be measured to determine the possible power output and to help in choosing equipment.Cost and availability: Estimate the size of generator needed to meet the energy demand, based on the head, flow and power outputs of available equipment. Typically, the higher the head the lower the cost per installed kilowatt. A typical system may cost approximately US$3,000 per kilowatt. The initial investment is high, but running costs, mostly maintenance, are low because there is no need to buy fuel. Viability: Comparing the likely annual income with capital cost gives a rough guide to financial viability. If the annual income is less than 10 per cent of the capital cost, the project is not viable. If it is 10-25 per cent the scheme could be possible. If the annual income is more than 25 per cent, then the scheme is viable.Head and flow: Decide on a suitable combination of head and flow to produce the required power. Assumptions should be made on the system efficiency, but if in doubt, assume an overall efficiency (water power to electrical power) of 45 per cent.Village meeting: Present the findings of the survey to the community at an open meeting. Local government staff and local development organisations should be encouraged to attend.Other steps: A number of other steps need to be taken, including a detailed site survey, finalising power output, producing a scale map and scheme layout, a detailed costing, consumer contracts for electricity supply and organising finance. Once this has been done the scheme can get under way. Ordering materials, installation and training can all be undertaken.

Measuring Power and Efficiency:

Power

Power is measured in Watts (W) or kilowatts (kW). There are 1000 W in 1 kW.

Pico hydro power has a maximum electrical power output of 5 kW.

There are three types of power when referring to a hydro project; water or hydraulic power, mechanical power and electrical power.

Hydraulic power will always be more than mechanical and electrical power because as power is converted from one form to another, some is lost at each stage of the process. See diagram below.

Up to 30% of power is lost in the penstock when water comes into contact with the walls of the pipe. This friction slows down the water, hence losing power.

The biggest loss usually occurs when the jet of water hits the turbine runner. This should be approximately 30% on a well designed system.

Approximately a further 20-30% will be lost in the generator when the mechanical power is converted into electricity.

Efficiency

Efficiency describes how well power is converted into from one form to another.

A turbine with an efficiency of 70% will convert 70% of the hydraulic power into mechanical power, with 30% being lost.

System efficiency is the combined efficiency of all processes together.

The system efficiency for electricity generation using pico hydro is typically between 40% - 50%.

Example

If there is found to be 2.8 kW of hydraulic power in a small stream, the electricity that could be expected is:

2.8 x 45% = 2.8 x 0.45 = 1.26 kW

Calculating hydraulic power

The hydraulic power in a stream can is calculated when the Head and the Flow have been measured. The formula for calculating hydraulic power is:

Power = Head (metres) x Flow (litres per second) x 9.81

Example

If the head = 60 m and the flow = 10 l/s then:

Power = 60 x 10 x 9.81 = 5886 watts or 5.9 kW

The pico-hydro project in Kenya has proven that this technology is both sustainable and affordable. Utilising a small spring to generate electricity, the communities of Kathamba and Thima now watch TV, listen to the radio and children can do homework at night knowing this technology is environmentally friendly. Money saved on buying kerosene and batteries can be used for other things, including children's education.

Further reading

Pico Hydro for Village Power: A Practical Manual for Schemes up to 5 kW in Hilly Areas
Phillip Maher and Nigel Smith
Free, Nottingham Trent University, 2001. Also available in Spanish.
This manual helps to overcome some of the problems of pico-hydro implementation by providing clear instructions for design and installation of schemes on a local level. Designs are recommended that emphasise simplicity, low maintenance and long-life expectancy. The manual is aimed at everyone interested in pico-hydro or rural electrification. It is particularly intended for those who are thinking about this technology for the first time and perhaps looking to implement such a scheme locally, for 'first time' engineers.

The Pico Power Pack: Fabrication and Assembly Instructions
Phillip Maher
Free, Nottingham Trent University, 2001
The Pico Power Pack is a design of water-powered turbine and generator unit that can be installed in regions where there is a head or drop of at least 20 metres. The pack is aimed at manufacturers to stimulate local production of recommended designs and increase availability. This manual is a complementary publication to Pico Hydro for Village Power.

Water Power for a Village Business
Adam Harvey and Nigel Smith
Free, Nottingham Trent University, 2001
Provides initial advice and ideas to help explore opportunities for harnessing power from streams and rivers. It contains information on a range of applications for water power, illustrated case studies and an introduction to estimating the power potential of a stream.

These manuals can be obtained for free by joining the Pico Hydro Network from the website or by contacting them directly.

The Micro-hydro Pelton Turbine Manual: Design, manufacture and installation for small-scale hydropower
Jeremy Thake
The Micro-hydro Pelton Turbine Manual is written to enble the reader to design and manufacture Pelton turbines with capacities from a few hundred Watts to around 100kw, though much of the information is relevant for larger units too. Aimed at readers with a general engineering workshop background, the emphasis is on simple technology, so that the turbines can be made in small workshops with basic engineering facilities. More advanced processes are discussed for those with access to better manufacturing facilities. As well as detailing all the important aspects of design, the book covers basic theory, turbine selection, manufacture, installation, testing and problem solving.
£25.95, ITDG Publishing, 2000, ISBN: 1853394602

Pumps as Turbines: A Users Guide
Arthur Williams
A practical handbook on the use of standard pump units as a low-cost alternative to conventional turbines for electricity generation in remote locations. For engineers and technicians designing and installing small water-power schemes.
£9.95, ITDG Publishing, 1995, ISBN: 1853392855